U.S. patent application number 10/872566 was filed with the patent office on 2004-12-30 for titanium material, production thereof, and exhaust pipe.
This patent application is currently assigned to Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.). Invention is credited to Urushihara, Wataru, Yamamoto, Kenji, Yashiki, Takashi.
Application Number | 20040265619 10/872566 |
Document ID | / |
Family ID | 33422220 |
Filed Date | 2004-12-30 |
United States Patent
Application |
20040265619 |
Kind Code |
A1 |
Yamamoto, Kenji ; et
al. |
December 30, 2004 |
Titanium material, production thereof, and exhaust pipe
Abstract
(1) A titanium material composed of a substrate of pure titanium
or titanium alloy and an aluminum-containing layer formed thereon
having a thickness no smaller than 1 .mu.m and containing no less
than 90 mass % aluminum or aluminum plus silicon. (2) A titanium
material composed of a substrate of pure titanium or titanium alloy
and an aluminum-containing layer formed thereon having a thickness
no smaller than 1 .mu.m and containing no less than 90 mass %
aluminum or aluminum plus silicon, with a layer of Al--Ti
intermetallic compound interposed between them. (3) A titanium
material as defined in (1) wherein the substrate contains 0.5-10
mass % aluminum. (4) A titanium material as defined in (1) wherein
that surface of the substrate with which the aluminum-containing
layer is in contact contains 20-50 atomic % nitrogen. (5) A
titanium material as defined in (1) wherein a layer of aluminum
nitride is formed in the interface between the substrate and the
aluminum-containing layer. (6) An exhaust pipe for two- or
four-wheeled vehicles which is made of the titanium material
defined above.
Inventors: |
Yamamoto, Kenji; (Kobe-shi,
JP) ; Urushihara, Wataru; (Kobe-shi, JP) ;
Yashiki, Takashi; (Osaka-shi, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
Kabushiki Kaisha Kobe Seiko Sho
(Kobe Steel, Ltd.)
Kobe-shi
JP
|
Family ID: |
33422220 |
Appl. No.: |
10/872566 |
Filed: |
June 22, 2004 |
Current U.S.
Class: |
428/651 ;
427/430.1; 428/660 |
Current CPC
Class: |
C23C 30/00 20130101;
Y10S 428/926 20130101; Y10T 428/12743 20150115; C23C 2/12 20130101;
C23C 28/021 20130101; Y10S 428/939 20130101; Y10T 428/12806
20150115; C23C 2/26 20130101; C23C 28/023 20130101 |
Class at
Publication: |
428/651 ;
428/660; 427/430.1 |
International
Class: |
B32B 015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 27, 2003 |
JP |
2003-185309 |
Apr 28, 2004 |
JP |
2004-133867 |
Claims
What is claimed is:
1. A titanium material comprising: a substrate of pure titanium or
titanium alloy; and an aluminum-containing layer formed at least
partly on the surface of the substrate, said aluminum-containing
layer having a thickness no smaller than 1 .mu.m and containing no
less than 90 mass % aluminum or aluminum plus silicon.
2. The titanium material as defined in claim 1, wherein the
aluminum-containing layer is formed directly on the substrate.
3. The titanium material as defined in claim 1, wherein the
aluminum-containing layer is formed indirectly on the substrate,
with a layer of Al--Ti intermetallic compound interposed between
them.
4. The titanium material as defined in claim 3, wherein the Al--Ti
intermetallic compound is Al.sub.3Ti.
5. The titanium material as defined in claim 3, wherein the layer
of Al--Ti intermetallic compound has an average thickness no
smaller than 0.5 .mu.m and no larger than 15 .mu.m.
6. The titanium material as defined in claim 1, wherein the
substrate is a titanium-based alloy containing 0.5-10 mass %
aluminum.
7. The titanium material as defined in claim 6, wherein the
substrate is a titanium-based alloy composed substantially of
aluminum and titanium.
8. The titanium material as defined in claim 1, wherein that
surface of the substrate with which the aluminum-containing layer
is in contact contains 20-50 atomic % nitrogen.
9. The titanium material as defined in claim 1, wherein a layer of
aluminum nitride is formed in the interface between the substrate
and the aluminum-containing layer.
10. The titanium material as defined in claim 1, wherein the
aluminum-containing layer is one which is formed by hot-dip
plating.
11. The titanium material as defined in claim 1, wherein the
aluminum-containing layer has a thickness such that, when the
thickness is measured at three points (14 mm apart) selected in the
lengthwise direction of the titanium material on the
aluminum-containing layer, the difference between the thickness at
the middle point and the thickness at the outer two points is no
larger than 30% of the thickness at the middle point.
12. A method for producing the titanium material defined in claim
11, said method comprising forming the aluminum-containing layer by
hot-dip plating, which involves the dipping of the substrate in a
plating bath of molten metal, in such a way that the substrate is
pulled up from the plating bath at a rate of 1-20 cm/s.
13. A method for producing the titanium material defined in claim
1, said method comprising forming the aluminum-containing layer by
hot-dip plating, which involves the dipping of the substrate in a
plating bath of molten metal, and subsequently performing shot
blasting with hard particles.
14. An exhaust pipe made of the titanium material defined in claim
1.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a titanium material, a
method for production thereof, and an exhaust pipe. More
particularly, the present invention relates to a titanium material
from which to make an exhaust pipe for two- or four-wheeled
vehicles.
[0003] 2. Description of the Related Art
[0004] By virtue of their higher specific strength than ordinary
steels, titanium alloys are making inroads in the field of
transportation, particularly automobiles requiring weight
reduction. One way under study to realize weight reduction is by
replacement of prevailing stainless steel exhaust pipes with
titanium alloy ones. Unfortunately, exhaust pipes get hot partly
above 500.degree. C. and titanium alloys (without special
treatment) are subject to rapid oxidation at such high
temperatures, which poses a problem with durability.
[0005] Some ideas have been proposed to improve the oxidation
resistance of titanium alloys. They include an aluminum-clad
titanium alloy material (Japanese Patent Laid-open No.
Hei-10-99976), a method for plating by vapor deposition with Al--Ti
alloy (Japanese Patent Laid-open No. Hei-6-88208), and a method of
forming a TiCrAlN film by PVD (Japanese Patent Laid-open No.
Hei-9-256138). Unfortunately, cladding involves complex processes,
which leads to high production cost and poor economy. In addition,
vapor deposition and PVD present difficulties in forming
oxidation-resistant film inside an exhaust pipe.
OBJECT AND SUMMARY OF THE INVENTION
[0006] The present invention was completed in view of the
foregoing. It is an object of the present invention to provide a
titanium material with good oxidation resistance and an exhaust
pipe made thereof, which will solve problems involved in the prior
art technology mentioned above.
[0007] The titanium material according to the present invention is
composed of a substrate of pure titanium or titanium alloy and an
aluminum layer no thinner than 1 .mu.m which contains no less than
90 mass % of aluminum or aluminum plus silicon. The aluminum layer
may be formed on the substrate directly or indirectly with a layer
of Al--Ti intermetallic compound interposed between them.
[0008] In the case where an intermediate layer is used, the Al--Ti
intermetallic compound should preferably be Al.sub.3Ti and the
layer thickness should be no smaller than 0.5 .mu.m and no larger
than 1.5 .mu.m on average.
[0009] The titanium material according to the present invention may
be embodied such that the substrate is a titanium alloy containing
aluminum in an amount of 0.5-10 mass %. In this case, the substrate
may be a titanium alloy composed substantially of aluminum and
titanium.
[0010] The titanium material according to the present invention may
be embodied such that the surface layer of the substrate with which
the aluminum-containing layer is in contact contains nitrogen in an
amount of 20-50 at %.
[0011] The titanium material according to the present invention may
be embodied such that an intermediate layer of aluminum nitride is
formed between the substrate and the aluminum-containing layer.
[0012] The titanium material according to the present invention may
be embodied such that the aluminum-containing layer is formed by
hot-dip plating.
[0013] The titanium material according to the present invention may
be embodied such that the aluminum-containing layer has a limited
thickness variation which is defined as follows. When the thickness
is measured at three points (14 mm apart) selected in the
lengthwise direction of the titanium material on the
aluminum-containing layer, the difference between the thickness at
the middle point and the thickness at the outer two points is no
larger than 30% of the thickness at the middle point. The titanium
material constructed in this way is obtained by forming the
aluminum-containing layer by hot-dip plating (which involves
dipping the substrate in a plating bath of molten metal). In this
case, the substrate should be pulled up from the plating bath at a
rate of 1-20 cm/s.
[0014] The titanium material according to the present invention may
be produced in such a way that the aluminum-containing layer is
formed by hot-dip plating (which involves dipping the substrate in
a plating bath of molten metal) and then subjected to shot blasting
with hard particles.
[0015] An exhaust pipe made of the titanium material of the present
invention is also within the scope of the present invention.
[0016] The titanium material according to the present invention is
superior in oxidation resistance and can be applied easily to the
pipe inside having a complex shape. Therefore, it will find use as
a material for durable exhaust pipes of two- or four-wheeled
vehicles.
[0017] The exhaust pipe according to the present invention, which
is made of the titanium material mentioned above, is light in
weight and has good oxidation resistance which leads to improved
durability.
[0018] The production method according to the present invention
gives a titanium material with outstanding oxidation
resistance.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a photograph showing the titanium material
pertaining to one embodiment of the present invention in which
there is an intermediate Al.sub.3Ti layer formed between the
titanium substrate and the aluminum-containing layer.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] The first aspect of the present invention covers a titanium
material which is composed of a substrate of pure titanium or
titanium alloy and an aluminum-containing layer no thinner than 1
.mu.m containing no less than 90 mass % aluminum or aluminum plus
silicon.
[0021] The titanium material is endowed with improved oxidation
resistance by the aluminum-containing layer which produces
anti-oxidant actions. For the aluminum-containing layer to
contribute to oxidation resistance, it should be in the form of a
layer no thinner than 1 .mu.m and containing no less than 90 mass %
aluminum or aluminum plus silicon, which is formed on the substrate
of pure titanium or titanium alloy. The reason for this is that
aluminum or an aluminum alloy with a high aluminum content
preferentially forms a compact aluminum oxide (which has a large
negative value of free energy of formation) in an oxidative
atmosphere at a high temperature, and this aluminum oxide functions
as a protective film which prevents further oxidation.
Incidentally, silicon is an element to improve oxidation resistance
and hence silicon contained in the aluminum-containing layer
improves its oxidation resistance. In the case where silicon is
contained in the aluminum-containing layer, the total amount of
aluminum and silicon should be no less than 90 mass % of the
aluminum-containing layer.
[0022] The aluminum-containing layer (or the oxidation resistance
improving layer) should contain aluminum or aluminum plus silicon
in an amount no less than 90 mass %. Any amount less than 90 mass %
is not enough to produce the desired effect of oxidation
resistance.
[0023] In the case where the aluminum-containing layer contains
silicon, the amount of silicon should preferably be 1-20 mass % of
the total amount (100 mass %) of aluminum plus silicon. With an
amount less than 1 mass %, silicon does not produce the effect of
improving oxidation resistance. With an amount more than 20 mass %,
silicon will present difficulties with the hot-dip plating by which
the aluminum-containing layer is formed. Therefore, it is most
desirable that silicon accounts for about 10% in the total amount
of aluminum and silicon.
[0024] The aluminum-containing layer (composed of aluminum alone or
aluminum plus silicon) may inevitably contain other elements than
aluminum and silicon. They include magnesium, copper, iron, etc.
(originating from hot-dip plating) and titanium (originating from
the substrate composed of pure titanium or titanium alloy).
[0025] The aluminum-containing layer should have a thickness no
thinner than 1 .mu.m; otherwise, it would have pinholes that cause
oxidation to the substrate. There is no upper limit to thickness
because it produces a better antioxidant effect in proportion to
thickness unless it has pinholes. However, an excessively thick
layer makes the substrate poor in workability. Therefore, an
adequate thickness should be less than about 100 .mu.m.
Incidentally, the thickness of the aluminum-containing layer should
be determined by an average of measurements at arbitrary points
(say, three points) along the cross section of the titanium
material.
[0026] The aluminum-containing layer should preferably be formed by
hot-dip plating, which is capable of forming a uniform layer on a
complex shape (such as the inside of a pipe) and is fairly
economical. Hot-dip plating offers another advantage of reducing
the natural oxide film on the surface of the substrate (of pure
titanium or titanium alloy) during dipping in molten aluminum,
thereby improving adhesion between the substrate and the
aluminum-containing layer. Hot-dip plating should preferably be
carried out such that the bath temperature is 700-800.degree. C.
and the dipping time is 5-20 minutes. However, this condition will
vary depending on the kind and heat capacity of the substrate.
[0027] In addition, it is also possible to form the
aluminum-containing layer on the substrate by coating the substrate
with an organic paint containing aluminum flakes.
[0028] As mentioned above, the titanium material pertaining to the
first aspect of the present invention is superior in oxidation
resistance and can be produced by hot-dip plating which permits the
oxidation resistance improving layer to be formed on a complex
shape (such as the inside of a pipe) easily and economically. In
other words, it helps solve problems with the conventional
technology and it exhibits outstanding oxidation resistance.
[0029] If the substrate of pure titanium or titanium alloy (which
are collectively referred to as titanium hereinafter) is to be
tightly covered with the aluminum-containing layer, it is necessary
to clean the substrate surface of oxide film. Titanium is usually
covered with natural oxide film which has a thickness of tens of
nanometers. Dipping titanium in molten aluminum at a high
temperature removes oxide film by reduction reaction represented by
3TiO.sub.2+2Al.fwdarw.2Al.sub.2O.sub.3+3Ti. Simple dipping may not
provide sufficient adhesion. In this case, good adhesion is
obtained by repeating dipping in the plating bath of molten
aluminum, because such repeated dipping forms an Al--Ti
intermetallic compound by reaction between titanium and molten
aluminum. In other words, it is possible to achieve high adhesion
between the substrate and the aluminum-containing layer if the
substrate is previously covered with a layer of Al--Ti
intermetallic compound and then the aluminum-containing layer is
formed thereon.
[0030] Removal of natural oxide film by reduction may be
accomplished by, for example, dipping the substrate in molten
aluminum so that that natural oxide film reacts with molten
aluminum. Therefore, if the substrate is dipped in molten aluminum
for a sufficiently long time, natural oxide film is removed by
reduction and then a layer of Al--Ti intermetallic compound is
formed.
[0031] The second aspect of the present invention covers a titanium
material which is composed of a substrate of pure titanium or
titanium alloy and an aluminum-containing layer no thinner than 1
.mu.m formed thereon which contains no less than 90 mass % aluminum
or aluminum plus silicon, with an interlayer of Al--Ti
intermetallic compound interposed between them. As compared with
the titanium material according to the first aspect of the present
invention, the one according to the second aspect of the present
invention is better in adhesion between the substrate and the
aluminum-containing layer. In other words, the interlayer ensures
firm adhesion with a minimum of adhesion failure.
[0032] The finding that outstanding adhesion is achieved when the
Al--Ti intermetallic compound is Al.sub.3Ti has lead to the third
aspect of the present invention. Thus, according to the third
aspect of the present invention, the titanium material defined in
the second aspect of the present invention is characterized in that
the Al--Ti intermetallic compound (in the layer of Al--Ti
intermetallic compound) is Al.sub.3Ti. This titanium material
exhibits outstanding adhesion for the reasons mentioned above.
[0033] Incidentally, Al--Ti intermetallic compounds include
Ti.sub.3Al, TiAl, and Al.sub.3Ti. The former two are so brittle
that they cause defective adhesion if they occur in the inter-face
between the substrate (of pure titanium or titanium alloy) and the
aluminum-containing layer. There has been known a method of
improving adhesion by cladding a titanium plate with an aluminum
foil and then forming an intermetallic compound in the interface by
heat treatment for solid-phase reaction. This conventional method,
however, permits the formation of Ti.sub.3Al and TiAl in the
interface, thereby causing defective adhesion.
[0034] The third aspect of the present invention requires that the
Al.sub.3Ti layer be formed on the substrate (titanium) or in the
interface between the substrate and the aluminum-containing layer.
The present inventors succeeded in forming the Al.sub.3Ti layer as
required. In other words, they succeeded in forming the Al.sub.3Ti
layer composed of Al.sub.3Ti alone (without Ti.sub.3Al and TiAl) in
the interface between the substrate and the aluminum-containing
layer by hot-dip plating, with the dipping time and bath
temperature adequately controlled. (The mechanism of reactions
involved is not known.) The dipping time and bath temperature for
molten aluminum vary depending on the mass of the substrate
(titanium) to be treated. The duration of dipping is about 2-10
minutes, and the bath temperature is about 700-800.degree. C.
[0035] According to the fourth aspect of the present invention, the
layer of Al--Ti intermetallic compound should preferably have an
average thickness no smaller than 0.5 .mu.m and no larger than 15
.mu.m. The thickness of the layer of Al--Ti intermetallic compound
(such as Al.sub.3Ti) can be controlled by adjusting the duration of
dipping and the bath temperature at the time of hot-dip plating. It
becomes larger in proportion to the duration of dipping and the
bath temperature. In the case of excessively large thickness, the
aluminum-containing layer (which is responsible for oxidation
resistance) becomes thin on account of mutual diffusion between the
substrate (titanium) and the aluminum-containing layer, and
adhesion of the aluminum-containing layer deteriorates. Therefore,
the layer of Al--Ti intermetallic compound should not be thicker
than 15 .mu.m. On the other hand, in the case of excessively small
thickness, the layer of Al--Ti intermetallic compound does not
improve adhesion as required. Therefore, the layer of Al--Ti
intermetallic compound should not be thinner than 0.5 .mu.m.
Incidentally, the thickness of the layer of Al--Ti intermetallic
compound is determined by an average of measurements at arbitrary
points (say, three points) along the cross section of the titanium
material. This measurement may be accomplished by observation under
an SEM (with a magnification of 5000). The composition (in terms of
the amount of Al and Ti) of the Al--Ti intermetallic compound may
be determined by EPMA, for example. Incidentally, the layer of
Al--Ti intermetallic compound should preferably have an average
thickness no smaller than 1 .mu.m and no larger than 5 .mu.m.
[0036] In the present invention, the substrate (of pure titanium or
titanium alloy) is not specifically restricted and it may largely
vary in composition. A substrate containing aluminum will exhibit
improved adhesion with the aluminum-containing layer responsible
for oxidation resistance. The improved adhesion prevents the
aluminum-containing layer from peeling off when the titanium
material is bent after the aluminum-containing layer has been
formed thereon. The content of aluminum in the substrate necessary
for improved adhesion is no less than 0.5 mass %. A content less
than 0.5 mass % is not enough for improved adhesion. With a content
exceeding 0.5 mass %, aluminum produces no effect on adhesion
improvement of but makes the substrate brittle. Therefore, the
aluminum content should be less than 10 mass %. Thus, the fifth
aspect of the present invention requires that the aluminum content
in the substrate should be 0.5-10 mass %.
[0037] In the case where the substrate contains 0.5-10 mass %
aluminum, the remainder of the constituents (other than aluminum)
should substantially be titanium, so that the resulting titanium
material has good workability. Thus, the sixth aspect of the
present invention requires that the substrate should be composed
substantially of titanium and aluminum. "Substantially" in this
case means that titanium may be a titanium alloy containing
inevitable impurities.
[0038] The titanium material according to the present invention may
be composed of a substrate and an aluminum-containing layer such
that (1) the surface (and its vicinity) of the substrate with which
the aluminum-containing layer is in contact contains as much
nitrogen as 20-50 atomic % or (2) a layer of aluminum nitride is
formed in the interface between the substrate and the
aluminum-containing layer. Such construction prevents reactions due
to mutual diffusion between the substrate and the
aluminum-containing layer. This reduces the loss of the
aluminum-containing layer and maintains the effect of oxidation
resistance for a long period of time. That is, in this way, the
titanium material keeps its good oxidation resistance for a long
period of time. The mechanism for improvement in oxidation
resistance is as follows.
[0039] An ordinary substrate (other than those mentioned above)
having the aluminum-containing layer in direct contact therewith
permits mutual diffusion of elements between the substrate and the
aluminum-containing layer at high temperatures. As the result after
a long time, the aluminum-containing layer disappears or oxidation
resistance is lost. This is not the case if the surface of the
substrate contains nitrogen even though the substrate is in direct
contact with the aluminum-containing layer. The reason for this is
that elements in the substrate and elements in the
aluminum-containing layer mutually diffuse at high temperatures.
This thermal diffusion brings about reaction between nitrogen in
the surface layer of the substrate and aluminum in the
aluminum-containing layer, thereby giving rise to a layer of
aluminum nitride in the interface between the substrate and the
aluminum-containing layer. This aluminum nitride layer prevents the
further diffusion of elements between the substrate and the
aluminum-containing layer.
[0040] As mentioned above, nitrogen contained in the surface layer
of the substrate forms at high temperatures an aluminum nitride
layer in the interface between the substrate and the
aluminum-containing layer. The aluminum nitride layer may be
naturally formed while the titanium material (with an
aluminum-containing layer formed thereon) is being used at high
temperatures. It may also be intentionally formed by forming an
aluminum-containing layer on the substrate and then performing heat
treatment. If the content of nitrogen in the surface layer of the
substrate is less than 20 atomic %, the resulting aluminum nitride
layer does not achieve its object for protection. The upper limit
of nitrogen content is 50 atomic %, because titanium becomes
saturated with 50 atomic % nitrogen in the form of TiN.
Incidentally, the titanium material composed of a substrate and an
aluminum-containing layer formed thereon, which is not yet heated,
has a nitrogen-containing layer on the substrate but has no
aluminum nitride layer due to thermal diffusion and there exists an
extremely thin layer of nitrogen in the interface between the
substrate and the aluminum-containing layer.
[0041] Thus, the titanium material according to the seventh aspect
of the present invention is characterized in that the surface layer
of the substrate with which the aluminum-containing layer is in
contact contains as much nitrogen as 20-50 atomic %. And, the
titanium material according to the eighth aspect of the present
invention is characterized in that an aluminum nitride layer is
formed in the interface between the substrate and the
aluminum-containing layer.
[0042] As will be apparent from the foregoing, the titanium
material pertaining to the eighth aspect of the present invention
offers the following advantages. The aluminum nitride layer
functions as a protective layer that prevents mutual diffusion of
elements between the substrate and the aluminum-containing layer.
This protective layer retains the aluminum-containing layer and
good oxidation resistance. For this reason, the titanium material
has improved oxidation resistance, keeps good oxidation resistance
in a high-temperature atmosphere, and keeps good oxidation
resistance for a long period of time.
[0043] As will be apparent from the foregoing, the titanium
material pertaining to the seventh aspect of the present invention
offers the following advantages. An aluminum nitride layer is
formed in the interface between the substrate and the
aluminum-containing layer while the titanium material is being used
at high temperatures. The aluminum nitride layer functions as a
protective layer that prevents mutual diffusion of elements between
the substrate and the aluminum-containing layer. This protective
layer retains the aluminum-containing layer and good oxidation
resistance. For this reason, the titanium material has improved
oxidation resistance, keeps good oxidation resistance in a
high-temperature atmosphere, and keeps good oxidation resistance
for a long period of time. Incidentally, the titanium material on
which the aluminum nitride layer is not yet formed is composed of a
substrate (whose surface layer contains nitrogen) and an
aluminum-containing layer. The titanium material on which the
aluminum nitride layer has been formed is composed of a substrate
(whose surface layer contains nitrogen or does not contain
nitrogen), an aluminum nitride layer, and an aluminum-containing
layer.
[0044] The amount of nitrogen in the surface layer of the substrate
may be determined by using EPMA in combination with any of Auger,
XPS, and SIMS.
[0045] The aluminum nitride layer formed by heat treatment should
have a thickness of tens of nanometers to several nanometers. The
one with an excessively small thickness does not produce the
barrier effect (to prevent mutual diffusion of elements between the
substrate and the aluminum containing layer). The one with an
excessively large thickness is poor in workability.
[0046] According to the present invention, the aluminum-containing
layer (to improve oxidation resistance) may be formed by surface
treatment. In other words, the titanium material of the present
invention may be said to be a surface-treated titanium material.
The method for surface treatment is not specifically restricted,
and various methods may be used. They include, for example, hot-dip
plating and coating with an organic paint containing aluminum
flakes. Incidentally, cladding with an aluminum sheet does not fall
under the category of surface treatment. There are many methods for
surface treatment to form the aluminum-containing layer. Hot-dip
plating is recommendable above all. Hot-dip plating is capable of
forming a uniform layer on any complex shape, such as the inside of
a pipe. It is also inexpensive and economical. Another advantage of
hot-dip plating is that when the substrate is dipped in molten
aluminum, natural oxide film on the surface of the substrate (of
pure titanium or titanium alloy) is reduced, which provides good
adhesion between the substrate and the aluminum-containing layer.
Moreover, hot-dip plating forms a layer of Al--Ti intermetallic
compound on the substrate under certain conditions (such as
duration of dipping in molten aluminum). Therefore, a single step
of hot-dip plating can yield the titanium material pertaining to
the second aspect of the present invention or the titanium material
pertaining to the third and fourth aspects of the present
invention. For this reason, it is desirable that the
aluminum-containing layer should be formed by hot-dip plating
according to the ninth aspect of the present invention.
[0047] According to the present invention, hot-dip plating is
recommended as one way of forming the aluminum-containing layer.
The resulting aluminum-containing layer varies in its
characteristic properties (such as adhesion and thickness)
depending on the duration of dipping as well as the rate at which
the substrate is pulled up from the plating bath. Therefore, it is
desirable that the titanium substrate should be pulled up from the
plating bath at a rate of 1-20 cm/s according to the eleventh
aspect of the present invention. The reason for this is explained
below.
[0048] Hot-dip plating forms the aluminum-containing layer which
varies in thickness depending on position if the substrate is
pulled up at an exceedingly high rate. As the substrate is pulled
up, molten aluminum sticking to the substrate flows downward until
the substrate gets cooled. Thus, the resulting film is thicker at
the lower part than at the upper part.
[0049] If the rate of pulling up is lower than 20 cm/s, molten
aluminum flows down faster than this rate and returns to the
plating bath. Thus, no difference occurs in thickness between the
upper and lower parts of the substrate. For this reason, it is
desirable that the substrate should be pulled up at a rate lower
than 20 cm/s.
[0050] If the rate of pulling up is 1 cm/s, it takes 100 seconds
for a 1-meter long substrate to be pulled up. This means that the
duration of dipping greatly varies from the upper part to the lower
part. (The duration of dipping is usually 1-2 minutes.) Prolonged
dipping promotes reaction between the titanium substrate and the
molten aluminum, thereby reducing the thickness of the titanium
substrate. For this reason, the rate of pulling up should be larger
than 1 cm/s.
[0051] Moreover, the rate of pulling up should preferably be in the
range of 2-15 cm/s, so as to reduce variation in coating thickness
and to prevent the titanium substrate from getting thin.
[0052] In the case where the titanium substrate is pulled up from
the plating bath at a rate of 1-20 cm/s as mentioned above, the
aluminum-containing layer formed thereon has limited variation in
thickness from the upper part to the lower part. The thickness
variation is defined as follows. When the thickness is measured at
three points (14 mm apart) selected in the lengthwise direction of
the titanium material on the aluminum-containing layer, the
difference between the thickness at the middle point and the
thickness at the outer two points is no larger than 30% of the
thickness at the middle point. The titanium material as specified
above has the aluminum-containing layer formed thereon which is
uniform in thickness. Therefore, it has uniform oxidation
resistance and accurate thickness, as the tenth aspect of the
present invention defines.
[0053] The aluminum-containing layer formed by hot-dip plating
might have voids or might be discontinuous, which varies depending
on the state of the substrate and the rate of pulling up of the
substrate from the plating bath. While solidifying on the titanium
substrate, molten aluminum reacts with atmospheric air to form a
thin oxide film on its outer surface. This oxide film diminishes
the surface gloss. The present inventors conducted extensive
studies to tackle this problem. As the result, it was found that
the aluminum-containing layer is recovered from defects (such as
voids and discontinuous parts) if it undergoes shot blasting with
hard particles (such as tiny glass or metal balls) after it has
been formed by hot-dip plating. This leads to improved oxidation
resistance. It was also found that such shot blasting removes the
surface oxide film and imparts a metallic luster to the surface.
The oxide film to be removed by shot blasting is much thicker than
natural oxide film because it involves the oxide film formed on the
surface of molten aluminum when the substrate is pulled up from the
plating bath. After such a thick oxide film has been removed by
shot blasting, a very thin natural oxide film is formed, which does
not impair the glossy surface.
[0054] Therefore, according to the twelfth aspect of the present
invention, it is desirable that the aluminum-containing layer
should undergo shot blasting with hard particles after it has been
formed by hot-dip plating. Such shot blasting remedies defects in
the aluminum-containing layer, thereby improving its oxidation
resistance. Moreover, such shot blasting removes surface oxide
film, thereby producing a metallic luster.
[0055] The shot blasting mentioned above employs hard particles
with a higher hardness than aluminum. However, excessively hard
particles abrade the aluminum-containing layer. An adequate
hardness of the hard particles should be lower than the hardness of
alumina, preferably lower than the hardness of glass. The hard
particles should have a particle size of #100, which is common to
ordinary shot blasting. This particle size is equivalent to a
particle diameter of hundreds of micrometers. A particle diameter
larger than 10 .mu.m is desirable, because excessively small
particles do not effectively fill voids by impact. Shot blasting
may be accomplished most easily by ejecting hard particles by
compressed air. The air pressure should be lower than 5
kg/cm.sup.2, preferably lower than 3 kg/cm.sup.2. Shot blasting
with an excessively high air pressure scrapes off the
aluminum-containing layer.
[0056] As mentioned above, the titanium material pertaining to the
first to tenth aspects of the present invention is superior in
oxidation resistance and is obtained by surface treatment (such as
hot-dip plating) which permits the oxidation resistance layer to be
formed economically and easily on a complex shape such as the
inside of a pipe. Therefore, it will find use as a constituent of
the durable exhaust pipe for two- and four-wheeled vehicles, as
defined in the thirteenth aspect of the present invention.
[0057] In the case where the titanium material of the present
invention is applied to the exhaust pipe, it is desirable that the
aluminum-containing layer should be formed on both sides of the
exhaust pipe. In addition, the aluminum-containing layer may be
formed before or after the substrate has been formed into a
pipe.
EXAMPLES
[0058] The invention will be described in more detail with
reference to the following Examples and Comparative Examples, which
are not intended to restrict the scope thereof. Various changes and
modifications may be made in the invention without departing from
the spirit and scope thereof.
Example 1 and Comparative Example 1
[0059] Samples of the titanium material with an aluminum-containing
layer (for oxidation resistance) having the composition shown in
Table 1 were prepared from a substrate of pure titanium (JIS Type
1, 1 mm thick) by hot-dip plating, vapor deposition, or spraying
with a paint containing aluminum particles. To form the
aluminum-containing layer, hot-dip plating was accomplished by
dipping the substrate in molten aluminum such that the bath
temperature was 700-750.degree. C. and the duration of dipping was
5-20 minutes.
[0060] Not all the samples have an interlayer of Al--Ti
intermetallic compound which is formed in the interface between the
substrate and the aluminum-containing layer. Each sample was
analyzed by EPMA to see if the interlayer exists.
[0061] Incidentally, Table 1 shows (in the column of composition)
the composition of the aluminum-containing layer. The designation
of Al.sub.100 for Sample Nos. 2 and 3 indicates that they are
composed of 100 mass % aluminum and inevitable impurities. The
designation of Al.sub.95Ti.sub.5 for Sample No. 4 indicates that it
is composed of 95 mass % aluminum and 5 mass % titanium and
inevitable impurities. The designation of Al.sub.95Si.sub.5 for
Sample No. 6 indicates that it is composed of 95 mass % aluminum
and 5 mass % silicon and inevitable impurities. Other compositions
in Tables 2 and 3 should be interpreted in the same way as
above.
[0062] The composition of the aluminum-containing layer may be
adjusted by regulating the amount of silicon or iron to be added to
the plating bath in the case of hot-dip plating or by regulating
the amount of components to be evaporated in the case of vapor
deposition.
[0063] The titanium materials obtained in this manner were exposed
to the atmosphere at 800.degree. C. for 100 hours for
high-temperature oxidation test. Their thickness was measured
before and after the test, and the loss of thickness due to
oxidation was calculated. In this way the samples were evaluated
for oxidation resistance. The high-temperature oxidation test was
also performed on pure titanium in the same way as mentioned above
so as to evaluate its oxidation resistance.
[0064] The results are shown in Table 1. It is noted from Table 1
that Sample No. 1 (pure titanium without the oxidation resistance
layer) decreased in thickness by 200 .mu.m due to oxidation by the
high-temperature oxidation test. This suggests poor oxidation
resistance. Sample No. 5 (for comparison) decreased in thickness by
150 .mu.m . This suggests a slight improvement in oxidation
resistance.
[0065] By contrast, Sample No. 7 decreased in thickness by less
amount. This suggests good oxidation resistance. Sample Nos. 2, 3,
4, 6, and 8 decreased in thickness by much smaller amount. This
suggests very good oxidation resistance.
[0066] It is noted that Sample Nos. 2, 3, 4, 6, and 8 have better
oxidation resistance (or suffers less decrease in thickness)
according as the total amount of aluminum and silicon (or the
amount of aluminum alone if silicon is not contained) increases in
the aluminum-containing layer.
[0067] It is noted that Sample No. 5 (for comparison), which
contains an excessively large amount of titanium in the
aluminum-containing layer, greatly decreased in thickness because
coarse titanium oxide preferentially crystallized out in place of
protective aluminum oxide.
Example 2
[0068] Samples of the titanium material with an aluminum-containing
layer (for oxidation resistance) were prepared from a substrate of
pure titanium (JIS Type 1, 1 mm thick) and a substrate of titanium
alloy containing aluminum (with varied aluminum content) by hot-dip
plating. The aluminum-containing layer has the composition
represented by Al.sub.100 as shown in Table 2; that is, it is
composed of 100 mass % aluminum. Hot-dip plating was accomplished
in the same way as in Example 1. In Table 2, the column of
substrate shows the composition of the substrate. The designation
of Ti-1.5Al indicates that the substrate is a titanium alloy
composed of titanium and 1.5 mass % aluminum, with the balance
being inevitable impurities. Other compositions in Tables 2 and 3
should be interpreted in the same way as above.
[0069] The titanium material obtained in this manner underwent
90.degree. bending test that causes peeling at the corner. Adhesion
between the substrate and the aluminum-containing layer was
evaluated from the degree of peeling.
[0070] The titanium material which had undergone 90.degree. bending
test underwent the high-temperature oxidation test in the same way
as in Example 1. Oxidation resistance of the sample was evaluated
in the same way as mentioned above.
[0071] The results are shown in Table 2. It is noted from Table 2
that Sample No. 6 (for comparison), in which the substrate is a
titanium alloy represented by Ti-15Al (composed of titanium and 15
mass % aluminum), suffered cracking in the substrate in the bending
test. It is also noted that Sample No. 1, in which the substrate is
pure titanium, did not suffer cracking in the substrate but
suffered peeling.
[0072] By contrast, Sample Nos. 2 to 5, in which the substrate is a
titanium alloy containing 0.5-10 mass % aluminum, did not suffer
peeling in the bending test. This suggests good adhesion between
the substrate and the aluminum-containing layer.
[0073] Incidentally, all of Sample Nos. 2 to 5 are found to be
superior in oxidation resistance with very little loss in
thickness. They are almost the same in oxidation resistance with a
small difference in thickness decrease.
Example 3
[0074] A substrate of pure titanium (JIS Type 1, 1 mm thick) and a
substrate of Ti-1.5Al alloy underwent ion nitridation so that a
nitrogen-containing layer was formed on the outer surface of the
substrate. The content of nitrogen in the nitrogen-containing layer
was varied and determined by EPMA.
[0075] Samples of the titanium material with an aluminum-containing
layer (for oxidation resistance) were prepared by hot-dip plating
from the substrate on which the nitrogen-containing layer had been
formed. The aluminum-containing layer has the composition
represented by Al.sub.100 as shown in Table 3; that is, it is
composed of 100 mass % aluminum. Hot-dip plating was accomplished
in the same way as in Example 1.
[0076] The titanium materials obtained in this manner were examined
for oxidation resistance by the high-temperature oxidation test in
the same way as in Example 1. In some samples, a layer of aluminum
nitride is formed in the interface between the substrate and the
aluminum-containing layer during heating in the high-temperature
oxidation test. To confirm the presence or absence of the aluminum
nitride layer, a sample of the same titanium material as mentioned
above was heated in the same way as in the high-temperature
oxidation test and then cooled, and the cross section of the cooled
sample was examined with a TEM (transmission electron
microscope).
[0077] The results are shown in Table 3. It is noted from Table 3
that Sample Nos. 1 and 7, which had no nitrogen-containing layer on
the surface layer of the substrate, formed no aluminum nitride
layer at all in the interface between the substrate and the
aluminum-containing layer (for oxidation resistance) in the
high-temperature oxidation test, regardless of whether the
substrate is pure titanium or Ti-1.5Al alloy. It is also noted that
Sample Nos. 2, 3, 8 and 9 did not form aluminum nitride layer in
the interface between the substrate and the aluminum-containing
layer during the high-temperature oxidation test, if the nitrogen
content is 2-15 atomic % (not meeting the requirement for 20-50
atomic %) in the nitrogen-containing layer on the surface of the
substrate.
[0078] Sample Nos. 2, 3, 8, and 9 decreased in thickness due to
oxidation by the high-temperature oxidation test as shown in Table
3.
[0079] By contrast, Sample Nos. 4 to 6 and 10 to 12 gave rise to an
aluminum nitride layer in the interface between the substrate and
the aluminum-containing layer during heating in the
high-temperature oxidation test, because a nitrogen-containing
layer containing 27-48 atomic % nitrogen (which meets the
requirement for 20-50 atomic %) is formed on the surface of the
substrate.
[0080] Sample Nos. 4 to 6 and 10 to 12 gave the results in the
high-temperature oxidation test as shown in Table 3. Sample Nos. 4
to 6 and 10 to 12 are superior in oxidation resistance (with a
small thickness decrease due to oxidation in the high-temperature
oxidation test) to Sample Nos. 2, 3, 8, and 9, in which the
nitrogen-containing layer is absent or the nitrogen content in the
nitrogen-containing layer is 2-15 atomic %.
[0081] These titanium materials (Sample Nos. 4 to 6, and 12 to 12)
increase in oxidation resistance and decrease in loss of thickness
due to oxidation in the high-temperature oxidation test according
as the content of nitrogen increases in the nitrogen-containing
layer formed on the surface of the substrate.
Example 4 and Comparative Example 2
[0082] Samples of the titanium material with an aluminum-containing
layer (for oxidation resistance) were prepared from a substrate of
pure titanium (JIS Type 1, 1 mm thick) by hot-dip plating. Hot-dip
plating was accomplished by dipping the substrate in molten
aluminum such that the bath temperature was 750.degree. C. and the
duration of dipping ranged from 0.1 to 60 minutes. Not all the
samples have an interlayer of Al--Ti intermetallic compound which
is formed in the interface between the substrate and the
aluminum-containing layer. Each sample was analyzed by EPMA (in the
same way as in Example 1) to see if the interlayer exists.
[0083] The substrate of pure titanium was clad with an aluminum
sheet to give an aluminum-clad titanium material. This product was
heated in the atmosphere at 500.degree. C. for 60 minutes to form a
layer of Al--Ti intermetallic compound in the interface between the
substrate (of pure titanium) and the aluminum sheet. The resulting
product was examined for elemental analysis by EPMA in the same way
as mentioned above in order to confirm the presence of the layer of
intermetallic compound.
[0084] The thus obtained titanium material underwent 900 bending
test. Adhesion between the substrate and the aluminum-containing
layer or the aluminum sheet was evaluated from the degree of
peeling at the corner.
[0085] After the bending test, the titanium material under-went the
high-temperature oxidation test (in the atmosphere at 800.degree.
C. for 100 hours) in the same way as in Example 1. The oxidation
resistance of the sample was evaluated from the amount of decrease
in thickness at the bent part due to oxidation in the
high-temperature oxidation test.
[0086] The results are shown in Table 4. FIG. 1 is an electron
micrograph showing the interface (and its vicinity) between the
substrate and the aluminum-containing layer. This photograph was
taken after hot-dip plating and before bending test. The specimen
for FIG. 1 was taken from Sample No. 3 specified in Table 4. It is
noted from FIG. 1 that the titanium material is composed of the
substrate and the aluminum-containing layer, with the interlayer of
Al.sub.3Ti interposed between them.
[0087] It is noted from Table 4 that Sample No. 1, which was
produced by dipping the substrate (of pure titanium) in the plating
bath for 0.1 minutes, did not give a layer of intermetallic
compound in the interface between the substrate and the
aluminum-containing layer, and it also retained an oxide film on
the surface of the substrate.
[0088] By contrast, Sample Nos. 2 to 6 and 8, for which the
duration of dipping was extended, gave a layer of intermetallic
compound (Al.sub.3Ti) in the interface between the substrate and
the aluminum-containing layer. It is also noted that the Al.sub.3Ti
layer becomes thicker according as the during of dipping
increases.
[0089] Sample No. 1, which lacks the layer of Al--Ti intermetallic
compound in the interface between the substrate and the
aluminum-containing layer, suffered peeling in the bending test. By
contrast, Sample Nos.2 to 6 had a layer of Al.sub.3Ti in the
interface between the substrate and the aluminum-containing layer.
The layer of Al.sub.3Ti had a thickness of 1-10.5 .mu.m (which
meets the requirement for the average thickness of 0.5-15 .mu.m).
It also exhibited good adhesion with the substrate without peeling
in the bending test. Sample No. 8, however, had a layer of
Al.sub.3Ti in the interface between the substrate and the
aluminum-containing layer. The layer of Al.sub.3Ti had a thickness
of 20 .mu.m (which does not meet the requirement for the average
thickness of 0.5-15 .mu.m). Therefore, it suffered partial peeling
in the bending test.
[0090] Sample No. 7 is an aluminum-clad titanium material, which
has a layer (8.6 .mu.m thick) of Al--Ti intermetallic compound
(including Ti.sub.3Al, TiAl, and Al.sub.3Ti) in the interface
between the substrate (of pure titanium) and the aluminum sheet.
This titanium material suffered partial peeling in the bending
test.
[0091] After the bending test, the titanium material under-went the
high-temperature oxidation test, which gave the results as shown in
Table 4. As compared with Sample No. 7 (aluminum-clad titanium
material), Sample Nos. 2 to 6 exhibited better oxidation resistance
with a less amount of thickness decrease in the high-temperature
oxidation test. This suggests that Sample Nos. 2 to 6 are superior
in oxidation resistance as well as adhesion between the substrate
and the aluminum-containing layer.
[0092] Sample Nos. 3 and 4 are particularly superior in oxidation
resistance because the Al.sub.3Ti layer has a thickness of 2.5-4.5
.mu.m, which meets the requirement for the thickness from 1 to 5
.mu.m . This suggests that Sample Nos. 3 and 4 are particularly
superior in oxidation resistance as well as adhesion between the
substrate and the aluminum-containing layer.
[0093] It is noted that Sample Nos. 2 to 4 increase in oxidation
resistance in proportion to the thickness of the Al.sub.3Ti
layer.
[0094] Incidentally, Sample No. 1 in Table 4 is similar or
identical in structure to Sample No. 1 in Table 2 and Sample Nos. 3
to 5 in Table 1. Therefore the former exhibits as good oxidation
resistance as the latter before the bending test which is carried
out after the aluminum-containing layer has been formed by hot-dip
plating. However, it is noted in Table 4 that Sample No. 1 is poor
in oxidation resistance (with a large amount of thickness decrease)
in the high-temperature oxidation resistance test which follows the
bending test. The reason for this is that the sample suffered
peeling in the bending test and the sample with peeling underwent
the high-temperature oxidation resistance test which causes
thickness decrease by oxidation.
Example 5 and Comparative Example 3
[0095] A sheet of pure titanium (measuring 30 cm by 10 cm and 1 mm
thick) was dipped in molten aluminum (containing about 2% iron as
impurities) at a bath temperature of 700.degree. C. The titanium
sheet was pulled up in its lengthwise direction at a rate of
0.05-50 cm/s. The thus obtained titanium material was examined for
the thickness of the aluminum-containing layer at an upper part (1
cm away from the top), at an intermediate part (15 cm away from the
top), and at a lower part (29 cm away from the top).
[0096] The results are shown in Table 5. It is noted that the
aluminum-containing layer becomes thicker according as the rate of
pulling up from the plating bath increases. This tendency is more
noticeable in the lower part. In other words, the difference in
thickness increases in going downward.
[0097] In the case where the rate of pulling up is 50 cm/s, the
difference between the thickness at the upper part and the
thickness at the intermediate part is 31.2% [=100.times.(80-
55)/80] of the thickness at the intermediate part, and the
difference between the thickness at the intermediate part and the
thickness at the lower part is 150% of the thickness at the
intermediate part. In the case where the rate of pulling up is 30
cm/s, the difference between the thickness at the upper part and
the thickness at the intermediate part is 27.7% of the thickness at
the intermediate part, and the difference between the thickness at
the intermediate part and the thickness at the lower part is 38.5%
of the thickness at the intermediate part.
[0098] In the case where the rate of pulling up is 15 cm/s, the
difference between the thickness at the upper part and the
thickness at the intermediate part is 20% [=100.times.(55-44)/55]
of the thickness at the intermediate part, and the difference
between the thickness at the intermediate part and the thickness at
the lower part is 18.2% of the thickness at the intermediate part.
The percentage in the case of 15 cm/s is smaller than the
percentage in the case of 50 cm/s or 30 cm/s.
[0099] In the case where the rate of pulling up is 10 cm/s, the
difference between the thickness at the upper part and the
thickness at the intermediate part and the difference between the
thickness at the intermediate part and the thickness at the lower
part are smaller than those in the case where the rate of pulling
up is 15 cm/s. Likewise, in the case where the rate of pulling up
is 2 cm/s, the difference between the thickness at the upper part
and the thickness at the intermediate part and the difference
between the thickness at the intermediate part and the thickness at
the lower part are smaller than those in the case where the rate of
pulling up is 10 cm/s.
[0100] The rate of pulling up at 15 cm/s, 10 cm/s, or 2 cm/s meets
the requirement (specified in the eleventh aspect of the present
invention) that the titanium material should be pulled up from the
plating bath of molten metal at a rate of 1-20 cm/s. As is apparent
from the foregoing and Table 5, the samples meet the requirement
(specified in the tenth aspect of the present invention) that when
the thickness is measured at three points (14 mm apart) selected in
the lengthwise direction of the titanium material on the
aluminum-containing layer, the difference between the thickness at
the middle point and the thickness at the outer two points should
be no larger than 30% of the thickness at the middle point.
[0101] In the case where the rate of pulling up is 0.05 cm/s, the
difference between the thickness at the upper part and the
thickness at the intermediate part is 2% of the thickness at the
intermediate part, and the difference between the thickness at the
intermediate part and the thickness at the lower part is 6.1% of
the thickness at the intermediate part. In other words, the
aluminum-containing layer has a uniform thickness but the resulting
titanium material becomes thin due to excessive reaction between
the titanium substrate and aluminum because the during of dipping
greatly differs between the upper part and the lower part.
Example 6 and Comparative Example 4
[0102] A sheet of pure titanium (measuring 30 cm by 10 cm and 1 mm
thick) was dipped in molten aluminum (containing about 2% iron as
impurities) at a bath temperature of 700.degree. C. The titanium
sheet was pulled up in its lengthwise direction at a rate of 3
cm/s. The thus obtained titanium material underwent shot blasting
with glass beads (as hard particles). The air pressure for blasting
was 2 kg/cm.sup.2 and the duration of blasting was 10 seconds.
[0103] The titanium material which has undergone shot blasting is
designated as "titanium material A". For oxidation test, this
sample was exposed to the atmosphere at 800.degree. C. for 100
hours. The oxidation resistance of the sample was evaluated from
the change in mass measured before and after the oxidation test. A
second sample designated as "titanium material B" was prepared in
the same way as mentioned above except that it did not undergo shot
blasting. The oxidation resistance of this sample was evaluated in
the same way as mentioned above.
[0104] It was found that "titanium material B" gained a weight of 3
mg/cm.sup.2 due to oxidation, whereas "titanium material A" gains a
weight of 1.9 mg/cm.sup.2 due to oxidation. Apparently, the latter
is superior to the former in oxidation resistance.
[0105] These samples were examined for surface state by visual
observation. "Titanium material A" (with shot blasting) looked
better (owing to a metallic luster) than "titanium material B"
(without shot blasting).
1TABLE 1 Oxidation Decrease resistance Method Al-Ti in thickness
No. layer Composition of preparation layer (.mu.m) Example for 1
None -- -- -- 200 comparison 2 Al Al.sub.100 Hot-dip plating yes 50
-- 3 Al Al.sub.100 Spraying no 50 -- 4 Al-Ti Al.sub.95Ti.sub.5
Vapor deposition no 65 -- 5 Al-Ti Al.sub.85Ti.sub.15 Vapor
deposition no 150 comparison 6 Al-Si Al.sub.95Si.sub.5 Hot-dip
plating yes 52 -- 7 Al-Si Al.sub.85Si.sub.15 Hot-dip plating yes
125 -- 8 Al-Fe Al.sub.95Fe.sub.5 Hot-dip plating yes 60 --
[0106]
2TABLE 2 Oxidation resistance Method of Bending Decrease in No.
Substrate layer Composition preparation test thickness (.mu.m)
Example for 1 Pure Ti Al Al.sub.100 Hot-dip plating Peeled 50 -- 2
Ti-1.5Al Al Al.sub.100 Hot-dip plating Peeled 48 -- 3 Ti-3Al-2.5V
Al Al.sub.100 Hot-dip plating Peeled 46 -- 4 Ti-6Al-4V Al
Al.sub.100 Hot-dip plating Peeled 51 -- 5 Ti-6Al-2Sn-4Zr-2Mo Al
Al.sub.100 Hot-dip plating Peeled 48 -- 6 Ti-15Al Al Al.sub.100
Hot-dip plating Substrate Not evaluated comparison cracked
[0107]
3TABLE 3 Aluminum Oxidation Decrease in Content of nitrogen in
nitride resistance Method of thickness No. Substrate surface layer
(atomic %) layer layer Composition preparation (.mu.m) Example for
1 Ti-1.5Al 0 No Al Al.sub.100 Hot-dip plating 48 -- 2 Ti-1.5Al 2 No
Al Al.sub.100 Hot-dip plating 48 -- 3 Ti-1.5Al 15 No Al Al.sub.100
Hot-dip plating 42 -- 4 Ti-1.5Al 27 Yes Al Al.sub.100 Hot-dip
plating 31 -- 5 Ti-1.5Al 35 Yes Al Al.sub.100 Hot-dip plating 27 --
6 Ti-1.5Al 48 Yes Al Al.sub.100 Hot-dip plating 20 -- 7 Pure Ti 0
No Al Al.sub.100 Hot-dip plating 50 -- 8 Pure Ti 2 No Al Al.sub.100
Hot-dip plating 50 -- 9 Pure Ti 15 No Al Al.sub.100 Hot-dip plating
43 -- 10 Pure Ti 27 Yes Al Al.sub.100 Hot-dip plating 33 -- 11 Pure
Ti 35 Yes Al Al.sub.100 Hot-dip plating 29 -- 12 Pure Ti 48 Yes Al
Al.sub.100 Hot-dip plating 22 --
[0108]
4TABLE 4 Duration of Decrease in No. Substrate dipping (min) Al-Ti
compound Thickness Bending test thickness (.mu.m) 1 Pure Ti 0.1
None 0 Peeled 200 (with residual oxide film) 2 Pure Ti 3 Al.sub.3Ti
1 Not peeled 75 3 Pure Ti 5 Al.sub.3T 2.5 Not peeled 55 4 Pure Ti
20 Al.sub.3T 4.5 Not peeled 48 5 Pure Ti 45 Al.sub.3T 7.8 Not
peeled 67 6 Pure Ti 60 Al.sub.3T 10.5 Not peeled 75 7 Pure Ti --
Ti.sub.3Al, TiAl, Al.sub.3Ti 8.6 Partially peeled 175 8 Pure Ti 90
Al.sub.3T 20 Partially peeled 175 Remarks: No. 7 = Al-clad titanium
material
[0109]
5TABLE 5 Position where thickness is Rate of pulling up measured,
thickness in .mu.m (cm/s) Upper part Middle part Lower part 0.05 48
(0.97)* 45 52 (1.06)* 2 45 (0.9) 50 55 (1.1) 10 43 (0.82) 52 57
(1.1) 15 44 (0.8) 55 65 (1.18) 30 47 (0.72) 65 90 (1.38) 50 55
(0.68) 80 200 (2.5) Remarks: Ratio of the film thickness at the
upper or lower part to the film thickness at the middle part.
* * * * *